A reduced electron-extraction barrier at an interface between a polymer poly(3-hexylthiophene) layer and an indium tin oxide layer

► We characterize roles of the buried interface between P3HT and ITO by transient photovoltage (TPV). ► We observed a negative TPV in ITO/P3HT/Al, which demonstrates that ITO/P3HT contact is electron extracting. ► The theoretical study is conducted to reveal a reduced electron barrier by 0.5 eV for ITO/P3HT contact. ► Band bending and dipole formation are two possible reasons to reduce the electron barrier. ► The study paves a way to characterize the buried interface in solution processable optoelectronics.